In one type of inertial navigation system, three ring laser gyros are provided to sense rotations about three axes. In such a system, it would be desirable to utilize a single power supply to drive the three ring laser gyros. In general, a laser power supply must be capable of firing a laser, ie., of initiating current flow through a laser, and of sustaining current flow through the laser after it has fired. The voltage required to fire a laser is typically 2 to 3 times higher than the voltage required to sustain current once firing has occurred. Prior to firing, a laser presents essentially an open circuit to a power supply, whereas after firing, the voltage across the laser drops to a fixed value which is nearly independent of the laser current.
In the past, it has not been possible to reliably drive three lasers from a single power supply, because of small differences that invariably exist between the firing voltages of different lasers. If two or more lasers are connected to the same power supply, the production of a firing voltage by the power supply will cause the laser with the lowest firing voltage to fire first. When the first laser fires, the supply voltage will drop, thereby precluding the firing of the remaining lasers. One method of circumventing this problem is to use a power supply having a power output capability far in excess of that required to sustain operation of the lasers. However, this approach typically requires several attempts to start all lasers, and also results in large and potentially damaging input power surges when individual lasers fire.